Halaman

Senin, 09 Juli 2012

Monsoon Relief

Returning to our Littleton, Colorado, farm today, I found that early monsoon rains have revitalized the landscape. Indeed, over the past few days, heavy rains have moved northward across the Front Range, bringing much needed rain to the tinder-dry mountain forests and welcome moisture to the urban corridor. While some flooding, mudslides and sinkholes developed, the storms have reduced the wildfire risk to some degree and, so far, have not ignited any new fires.

The annual monsoon rains of the American Southwest result from a southerly flow that brings in moisture from both the Gulf of California and the Gulf of Mexico. The engine for this wind pattern is high pressure over the Southern Plains that generally develops by early July and persists through much of August; winds move clockwise around that atmospheric ridge, sweeping moisture northward along its western rim. Showers and thunderstorms are usually confined to the Desert Southwest and Four Corners Region early in the season, reaching the Colorado Front Range by late July and August. Thanks to the dome of drought that has plagued the south-central and southeastern U.S. for several weeks, the Monsoon got an early start and Colorado, caught in its own drought after a mild, snow-starved winter and a warm, dry spring, has received an early and very welcome gift.

Unfortunately, the monsoon flow will be shut off for the rest of this week as high pressure builds in from the West, bringing another round of hot, dry weather to the State and blocking the southerly stream of moisture. When the Southwest Monsoon might generate more relief is anyone's guess but its typical arrival date is still a week or two away.